Method and apparatus for sizing brake drum rings

ABSTRACT

Method and apparatus for sizing brake drum rings of frustoconical cross section wherein the ring is inserted axially into a female sizing die having a complementary frustoconical surface and moved axially relative to the die until squeezed sufficiently to take a permanent set while undergoing axial elongation as it is pushed into the sizing die. The deformation is controlled by the distance of ring entry into the die. The ring, after being sized, is ejected back out of the entrance of the die.

llnited States Patent 11 1 1111 3,805,300 Brede, HI et al. Apr. 23, 1974 [5 METHOD AND APPARATUS FOR SIZING 3,676,917 7/1972 Wayson et al. 29/4205 BRAKE DRUM RINGS 3,677,655 7/1972 Ratteree et all. 29/401 X [75] Inventors: r f: fi:?% g Primary Examiner-Charles W. Lanham Canaan both of conng Assistant Examiner-D. C. Reiley, III

Attorney, Agent, or Firm-Barnes, Kisselle, Raisch & [73] Assignee: Motor Wheel Corporation, Lansing, Cheats M1ch.

[22] Filed: Jan. 29, 1973 57] ABSTRACT PP ,309 Method and apparatus for sizing lbrake drum rings of frustoconical cross section wherein the ring is inserted 52 U.S. c1 29/401 29/4205 72/345 axially a female Sizing die having a 51 Int. c1...: B221 3/24 B2l d 45/00 my frustnical Surface and axially relative 58 Field of Search 29/401 4205- 72/344 to the die Squeezed sufficiemly to take a Perm 72/345 nent set while undergoing axial elongation as it is pushed into the sizing die. The deformation is con- [56] References Cited trolled by the distance of ring entry into the die. The

ring, after being sized, is ejected back out of the en- UNITED STATES PATENTS trance of the die R3,423 5/1869 Roberts 72/344 439,883 11/1890 Marcy 29/401 X 21 Claims, 6 Drawing Figures /O s \,411"'4O MIENTED APR 23 IQR SHEET 3 0F 3 METHOD AND APPARATUS FOR SIZING BRAKE DRUM RINGS This invention relates to vehicle brake drums and more particularly to an improved method and apparatus for sizing a sintered powder metal brake drum ring having a cylindrical inner periphery which forms a brake track and a frustoconical outer periphery.

A brake drum with a sintered metal drum ring having cylindrical inner and outer surfaces and fixed to a sheet metal backing plate is disclosed in United States Pat. No. 3,500,972. Another brake drum generally of this type having an improved frustoconical contour is disclosed in a copending United States patent application of Alexander Brede III, Charles E. Schalla and Frank R. Tully, Ser. No. 255,230, filed May 19, 1972 and assigned to the assignee herein.

In making drum rings of the same or similar configuration as that disclosed in said copending application Ser. No. 255,230, it has been found that after the drum ring has been compacted to high density and then sintered and allowed to cool the ring may have a small amount of distortion producing an out-of-round condition in the inner peripheral surface thereof. This surface must be held to within close circularity limits since it serves as the cylindrical brake track in the brake drum of which the ring is the chief component. This brake track surface may be brought into proper circularity or roundness by a machining operation, but this adds extra manufacturing cost and may introduce some unbalance into the drum, thereby tending to negate some of the advantages of forming the brake drum by powder metallurgy techniques.

Accordingly, it is an object of the present invention to provide improved method and apparatus which will enable an out-of-round brake drum ring having a frustoconical outer periphery to be sized in a rapid, accurate and economical manner to thereby reduce or eliminate out-of-roundness in the brake track surface of the drum ring.

Another object is to provide method and apparatus of the above character which will enable drum rings produced with the above configuration from compacted and'sintered metal powder to be sized after sintering without any scrap loss in a mass production operatlon.

In accordance with one embodiment of the invention, a blend of iron powder and graphite is compacted into a ring having a frustoconical outer periphery and a cylindrical inner periphery. After the compact has been sintered and cooled it is pressed endwise into a tapered female die in the direction of convergence of the die whereby the ring diameter is reduced by an amount that exceeds the elastic limit of the instered material in compression. This results in a permanent set in the material as it is cold worked by radial contraction and axial elongation in bringing the outer periphery of the ring essentially'to the die dimension at the end of sizing stroke. The circularity of the die is thus imparted throughout the ring to thereby reduce or eliminate the out-of-round condition of the ring.

Other objects, features and advantages of this invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings wherein:

FIGS. 1, 2, 3 and 4 are semi-schematic vertical sectional views alongthe axis of one exemplary but preferred embodiment of a drum ring sizing apparatus of the present invention and sequentially illustrating schematically the operation of the apparatus in accordance with the method of the invention.

FIG. 5 is a fragmentary vertical center section taken on the line 5-5 of FIG. 6 of one embodiment of a sizing die and press of the invention with the same shown in closed position at the end of the sizing stroke, corresponding to position of the parts shown in FIG. 3.

FIG. 6 is a horizontal plan view of the apparatus of FIG. 5 at two elevations.

Referring in more detail to the accompanying drawings, the method and apparatus of the invention is particularly adapted to size and/or remove an out-of-round condition from a brake drum ring 10 (FIG. 1) having a cylindrical inner peripheral surface 12, a frustoconical outer peripheral surface 14 and generally radially extending axially opposite end faces 16 and 18. Drum ring 10 is preferably compacted from a simple mixture of iron powder and graphite of relatively high density, in the order of 6.7 grams per cubic centimeter, in a compacting die set so that the configuration is essentially that of drum ring 10. The compact is sintered and then cooled, which may introduce a small amount of distortion into the sintered drum ring; i.e., the brake track surface 12 may have a slight ellipsoidal or oval shape with an unacceptable amount of out-ofroundness. This distortion can be removed by machining surface 12, but this is objectionable because it tends to negate one of the chief advantages of using powder metallurgy techniques; i.e., manufacturing complicated shapes to precise dimensions with little or no machining required. Machining to circularity also roughens the otherwise smooth finish imparted to surface 12 during the compacting operation, as well as imparting a possible unbalance to the ring in those cases where the distortion is of asymmetrical nature.

The aforementioned problems are overcome by the method and apparatus of the present invention, one preferred form of which, as illustrated schematically in FIGS. 14, includes a female sizing die 20 having a sizing cavity defined by a frustoconical surface 22 having a straight taper complementary to the outer periphery 14 of ring 10. Although not shown to scale in FIGS. l-4, the axial extent of die 20 is about twice that of ring 10. Die 20 is preferably oriented with its axis vertical with the large entrance end of the die cavity facing upwardly. The upper end surface 24 of the die 20 extends perpendicular to the axis of the die and is normally horizontal as indicated inFIGS. 1-4. The maximum diameter of surface 22, i.e., in the plane of surface 24, is greater than the outside diameter of surface 14 at end 18, and may be slightly less than, equal to or greater than the outside diameter of surface 14 at end 16 to permit fully insertion of ring 10 into the sizing cavity.

The sizing apparatus also includes a central piloting core 26 extending coaxially of die 22 and having a cylindrical outer periphery 28 which preferably is slightly smaller in diameter than the inside diameter of surface 12 of ring 10 after sizing. The upper end surface 30 of core 26 is preferably flat and horizontal so as to lie flush with surface 24 of die 20. In the example of the method and apparatus shown herein, both die 20 and core 26 are mounted in fixed relationship to one another and are maintained stationary throughout the operation of the apparatus. Preferably, the surface 28 of core 26 extends downwardly so as to be coextensive axially with surface 22.

The apparatus also includes an ejector 32 in the form of a cylindrical annulus mounted to move coaxially of and radially between die 20 and core 26 with its inside cylindrical surface 34 having a close clearance fit relative to surface 28, and with its outside cylindrical surface 36 having a close clearance fit with the lower edge of surface 22. Ejector 32 is adapted to move between a raised position shown in FIGS. 1 and 4, wherein its flat upper end surface 38 is flush with surfaces 24 and 30, and a lowered position wherein surface 38 is spaced below the leading' end surface 18 of ring (FIGS. 2 and 3).

The remaining principal component of the apparatus of the invention is a punch 40 mounted for movement coaxially of die from an elevated open position (FIGS. 1, 2 and 4) to a fully lowered position (FIG. 3).

, Punch 40 is also in the form of an annulus having inner and outer cylindrical surfaces 42 and 44 dimensioned similarly to the corresponding surfaces 34 and 36 of ejector 32. The lower end' surface 44 of punch 40 is preferably flat, or may be contoured to match the end surface 16 of ring 10, and thusin the example shown extends radially to make flat contact with surface 16.

The operation of the above-described embodiment of the apparatus of the invention is also explanatory of the method thereof. The cycle is normally begun with ejector 32 and punch 40 in their raised positions shown in FIG. 1. In this condition, concentric surfaces 24, 38 and form a flat supporting surface with only a slight annular gap therein (between the upper outside edge of ejector 32 and the upper inside edge of die 20) having a radial thickness dimension much smaller than the radial thickness of ring 10. Accordingly, ring 10 may be slidably supported on surface 24, as it is received from a conveyor or other transfer means, and slid endwise perpendicular to its axis from a position offset to one side of die 20 across surfaces 24, 38 and 30 it is approximately concentric with die 20. Due to the difference in the diametrical dimensions of surfaces 28 and 22 at the entrance end of the die cavity, this registering need only be approximate, allowing relatively large tolerances in any suitable pushing apparatus 41 employed to thus position ring 10 so that it is resting on ejector 32.

After ring 10 is positioned as shown in FIG. 1, the next step is to lower ejector 32 from its raised position of FIG. 1 to its lowered position as shown in FIG. 2. As ejector 32 begins its descent, ring 10 will drop by gravity with the ejector into the cavity of die 20 until the outer surface 14 of the ring makes initial seating contact with the sizing surface 22 of the die 20. In the example shown, this'condition is reached with ring 20 in the position shown in FIG. 2 wherein the ring has been inserted about two-thirds of its axial dimension into the die cavity. The extent of insertion of the ring into the cavity will, of course, vary depending upon the degree of out-of-roundness, diameter variation and/or distortion present in ring 10. The range of distortion in rings being received for sizing thus must be taken into account in deciding the entrance diameter of the die cavity. If desired, the axial extent of surface 22 may be increased so that the entrance diameter of the die cavity is equal to the maximum outside dimension of the drum ring having the greatest distortion. In such a case,

the drum rings when lowered for initial insertion into the die cavity will not reach initial seating contact until the ring has been at least fully inserted into the die cavity so that its upper surface 16 is flush with or below surface 24.

In the next step of the method, punch 40 is lowered in a smooth continuous stroke wherein its lower end face 44 contacts the end face 16 of ring 10 to force the ring axially a given distance along the wall 22 of the cavity of die 20. Due to the progressively increasing interference fit of the conical ring 10 with the conical surface 22, a radial compression force is applied inwardly of the drum ring progressively about its entire circumference and generally simultaneously along the entire axial length of the peripheral contact zones of the ring. Once the ring reaches circularity and thus has full contact with surface 22 this radial compression force causes the drum to yield radially inwardly. The distance of this axial movement into the die is calculated to cause the material of the ring to yield beyond its elastic limit such that cold flow of the material takes place. This in turn causes a slight decrease in the inside diameter of the ring (the diameter of surface 12) and also an axial elongation of the ring because the ring is not axially constrained other than by sliding friction with the wall 22. This axial elongation is taken into account in determining the lowered position of ejector 32 so that space exists between the upper surface 38 thereof and the lower end face 18 of the drum ring at the completion of the sizing stroke (FIG. 3).

In the next step of the method, punch 40 is lifted clear of ring 10 to its elevated position shown in FIG. 4 and then ejector 32 is raised from its position in FIG. 3 to its position in FIG. 4 to thereby reverse the axial forces applied to the ring. Due to the tapered surface 22 of the die cavity, as soon as ring 10 is moved a short distance upwardly from its position in FIG. 3, it will be uniformly released about its entire outer periphery from the wall 22, thereby facilitating ejection of the ring and minimizing die wear. When ring 10 has been raised to the position in FIG. 4, the pusher engages the outer periphery of the ring and slides the same horizontally in the direction of the arrow in FIG. 4 to clear the sizing die for reception of the next ring to be sized, whereupon the above-described sizing cycle is repeated on the next workpiece.

In accordance with one feature of the method of the invention, the axial dimension of surface 22 of the die cavity is established so that the trailing end surface 16 of ring 10 will be at least flush with and preferably slightly below the upper end surface 24 of die 20 by the time that the ring has progressed far enough axially into the die to enable the progressively increasing interference fit to bend the ring from its out-of-round shape to a true circle. In other words, in its first stage of axial forced travel into die 20, ring 10 is fully seated within the die cavity and in substantially complete engagement about its entire outer periphery with wall 22 before any radial compression of the ring takes place. Up to this point, only bending stresses are imposed on the ring, which normally constitute a stress below the elastic limit of the material, so that if the ring were ejected without further movement into the die it would spring back to its distorted out-of-round shape. Thus, to move the ring axially beyond the point of full seating in the die, the axial force exerted on the ring by punch 40 must be greatly increased which stresses it beyond its elastic limit so that it yields radially inwardly about its entire circumference a uniform small amount while also yielding axially to thereby elongate the ring. This cold working of the sintered material beyond the elastic limit in compression in its second stage of axial travel causes it to retain a set at substantially true circularity after the ring has been ejected from the die and relieved from the constraint thereof.

The uniform radial forces simultaneously imposed by the die along the entire outer surface of the ring during the second stage cold working step, with both the inner periphery l2 and the inner end 18 of the ring unrestrained, permitthe ring to change without imparting a taper and insuring that surface 12 is brought to a substantially cylindrical shape. The final inside dimension of surface 12 is preferably controlled by empirically testing the sample workpiece to determine the distance required to advance the workpiece from its fully seated condition to its fully sized and stressed position without surface 12 contacting surface 28. This obviates such problems as wearing of the pilot core 30 and seizure of the ring on the same.

It has been found that there is no appreciable change in the hardness of the workpiece due to the sizing method of the invention. Although there may be a low level of residual stress in the brake drum ring after sizing, no significant residual stresses have been detected, probably due to the self-relieving axially elongating action obtained in the sizing method.

Any suitable die lubricant may be used to lubricate the outer periphery 14 of the workpiece and the die cavity wall 22.

By way of description, and not by way of limitation, in one working example of the sizing of a brake drum ring in accordance with the present invention, a compacted and sintered drum ring compact 10 having the characteristics set forth below was sized as indicated below following the below-listed parameters:

Inside diameter of surface 12 prior to sizing, maximum and minimum 10.060 inches and 10.040 inches Axial distance between surfaces 16 and 18 befor and after sizing 2.58 inches Radial thickness of ring 10 at surface 16 after sizing 0.44 inch Radial thickness of ring 10 at surface 18 before and ft s z .Q-.. ..i nh .z

Composition of ring 10 in the powder state 1 part graphite, 1 part wax, and 99 parts of iron by weight before and Density of ring 10 as compacted ready for sintering 6.7 grams per c.c. Taper angle of a surface 14 before and after sizing 5 included angle Taper angle of surface 22 5 included angle Distance of axial travel of ring 10 from its fully seated to its fully sized position about 0.3 inch to 0.5 inch Maximum force exerted on ring 10 during sizing operation 70 tons It is to be understood for a workpiece of approximately the above size and characteristics, a reduction in diameter on the order of 0.050 inch to 0.100 inch has been found satisfactory as a measure of the work required to achieve permanent set and a roundness tolerance range of 0.005 inch. Preferably the outer contour of ring 10 is a straight taper, the minimum angle thereof being determined by the ejection force available taking into consideration the coefficient of friction of surface 14 relative to cavity wall 22. The maximum taper of surface 14 is determined by the limitations of press and die capacity and thus could be well in excess of the taper angle given in the example above, say up to about 15 included angle. Preferably surface 14 is smooth, but surfaces having ribs therein can be sized in the method of the invention if the ribs are uniformly spaced around the periphery and the crowns of the ribs extend axially from one end of the ring to the other along surface 14 or terminate at and merge into a smooth peripheral surface in flush relationship therewith.

Referring to FIGS. 5 and 6, a brake drum ring sizing press constructed pursuant to the presentinvention and capable of performing the above-described method of the invention is shown with like reference numerals applied to the components thereof corresponding to the components illustrated schematically in FIGS. l-4. Die 20 is seated in and detachably secured to a bolster 50 stationarily mounted on the bed or frame 52 of the press, and likewise pilot core 26 is detachably secured to bolster 50. Punch 40 is detachably secured to a platen 54 of the press so as to reciprocate vertically with the drive train of the press in a conventional manner. Suitable guide pins 56 may be provided to assure parallelism of punch 40 with the axis of die 20. The ejector 32 is raised and lowered on a series of actuator pins 58 which in turn rest on the platen 60 of a hydraulic ram 62 mounted beneath bed 52 of the press. The remaining details of the construction of the press as well as the appropriate control equipment to control the motion of the movable parts of the press in accor' dance with the operation described previously will be well understood by those skilled in the art and therefore not described in detail herein.

From the foregoing description it will now be apparent that the method and apparatus of the invention enable economical, reliable and efficient mass production sizing, rounding and/or finishing of sintered brake drum rings to accurate dimensions without requiring machining of the workpiece, thereby enhancing the uniformity, balance and finish of the product while also greatly reducing or eliminating scrap in the manufacture of brake drum rings.

It is to be understood that the above-described method and apparatus can be modified without departing from the present invention. For example, the apparatus of FIGS. 14 may be inverted, and core 26 eliminated, and die 20 arranged as the movable member to be brought downwardly onto ring 10 while the ring is stationarily supported on punch 40. Stripping may be then accomplished with ejector 32. As another example, ejector 32 can be yieldably lightly biased toward ring 10 to maintain contact therewith throughout the cycle so that ejector 32 can support the weight of ring 10 without exerting significant resistance to axial elongation of the ring. In addition, the size of the workpiece can vary as to the diameter of surface 12 from say 5 to 20 inches and axially from 2 to 10 inches, and the axial travel in the second stage may vary from about 0.2 to 2.0 inches.

We claim:

1. A method of sizing an out-of-round brake drum ring compacted and sintered from metal powder and having a frustoconical outer peripheral surface tapering linearly toward the axis of said ring toward one of the ends of said ring, comprising the steps of positioning the ring coaxially on a sizing die having a sizing cavity with a frustoconical peripheral surface tapered complementarily to said outer ring surface and of substantially perfect circularity for an axial distance exceeding the axial dimension of said ring, said cavity tapering from a diameter greater than to less than the outside diameter of said one end of said ring, bringing said ring into circularity by moving said ring and die axially relative to one another in the direction of increasing interference fit of said ring in said die cavity by applying axial force endwise to said ring and an opposing axial force to said die while leaving said ring unrestrained against movement in said direction except for the sliding frictional interengagement of said ring and cavity surfaces, terminating said movement after a predetermined relative axial travel of said ring along said cavity surface sufficient to first bend said outer peripheral surface of said ring into complete circumferential contact with said cavity surface throughout the axial extent of said ring surface and then to radially compress said ring beyond the elastic limit thereof and thereby cause it to take a permanent set as said ring conforms to the progressive reduction in diameter of said sizing cavity, and then reversing the relative movement of said ring and die to remove said ring from said die.

2. The method set forth in claim 1 wherein said cavity surface and said outer peripheral surface of said ring each have identical taper angles.

3. The method set forth in claim 1 wherein said ring is allowed to axially elongate in response to said radial compression thereof.

4. The method set forth in claim 3 wherein the inner periphery of said ring is cylindrical and comprises the brake track of said ring.

5. The method of claim 1 wherein the inner peripheral surface of said ring is maintained clear of any restraining apparatus during said relative axial motion in the direction of increasing interference fit.

6. The method set forth in claim 1 wherein said die is oriented with its axis generally vertical with its entrance end facing upwardly, and a pilot core is positioned concentrically within said die cavity to provide a flat end surface flush with a flat end surface of said die to form therewith a support surface extending perpendicular to the axis of said cavity, and wherein said step of positioning said ring includes sliding said ring on said one end thereof perpendicular to the ring axis along said support surface into coaxial registry with an annular cavity defined between said pilot core and said die cavity surface, the core piloting through said ring while said ring is being deformed by said die.

7. The method set forth in claim 6 wherein said increasing interference engagement travel of said ring in said die cavity is terminated while the inner periphery of said ring is spaced from said pilot core.

8. The method set forth in claim 6 wherein said positioning step further comprises elevating an ejector annulus within said cavity to bring an end surface of said ejector flush with said flat end surfaces, then sliding said ring into said registry to position the ring on said ejector end surface, and then lowering said ejector to lower said ring into engagement with the sizing surface of said die cavity.

9. The method set forth in claim 8 wherein said drum ring has a density of about 6.7 grams per cubic centimeter.

10. The method set forth in claim 1 wherein said taper angle of said outer periphery of said ring is in the order of five to fifteen degrees included angle.

11. The method set forth in claim 9 wherein said ring is made by compacting and sintering a metal powder blend comprising iron, graphite and wax and adpted to provide a pearlitic microstructure.

12. The method set forth in claim 11 wherein said drum ring has an inside diameter in the order of about five to twenty inches and an axial dimension in the order of 2 to 10 inches.

13. The method set forth in claim 12 wherein the relative axial travel of said ring and die is in the order of 0.2 to 2.0 inches.

14. The method set forth in claim 1 wherein said die is held stationary and said ring is moved into and out of the entrance of said die cavity to accomplish said relative axial movement in both of said directions.

15. A method of making a brake drum ring comprising the steps of compacting a brake drum ring from metal powder blend containing primarily iron powder into a ring shape having a trapezoid radial cross section with a frustoconical outer peripheral surface tapering linearly toward the axis of said ring toward one of the ends of said ring, sintering the ring compact and then cooling the same whereby said ring may be distorted to an out-of-round condition, positioning the ring coaxially in a sizing die cavity having a frustoconical peripheral surface tapered complementarily to said outer ring surface from a diameter greater than to less than the outside diameter of said one end of said ring and being of substantially perfect circularity for an axial distance exceeding the axial dimension of said ring, bringing said ring into circularity by moving said ring and die axially relative to one another in the direction of increasing interference fit of said ring in said die cavity by applying opposing axial forces endwise to said ring and said die while leaving said ring unrestrained against movement in said direction except for the sliding frictional interengagement of said ring and cavity surfaces, terminating said movement after a predetermined relative axial travel of said ring along said cavity surface sufficient to first bend said outer peripheral surface of said ring into substantially complete circumferential contact with said cavity surface throughout the axial extent of said ring surface and then to radially compress said ring beyond the elastic limit thereof and thereby cause it to take a permanent set as said ring conforms to the progressive reduction in diameter of said sizing cavity, and then reversing the relative movement of said ring and die to remove said ring from said die.

16. Apparatus for sizing an out-of-round brake drum ring compacted and sintered from metal powder and having a frustoconical outer peripheral surface tapering linearly toward the axis of the ring toward one of the ends of the ring, comprising a sizing die having a sizing cavity with a frustoconical peripheral surface tapered complementarily to the outer surface of the ring and of substantially perfect circularity for an axial distance exceeding the axial dimension of the ring, said cavity tapering from a diameter greater than to less than the outside diameter of said one end of the ring, means for moving said ring and die axially relative to one another in the direction of increasing interference fit of said ring in said die cavity, said moving means being adapted to apply axial force endwise to said ring and said die while leaving said ring unrestrained against movement in said direction except for the sliding frictional interengagement of said ring and cavity surfaces, said moving means being operable to terminate said movement after a predetermined relative axial travel of said ring along said cavity surface sufficient to first bend said outer peripheral surface of said ring into substantially complete circumferential contact with said cavity surface throughout the axial extent of said ring surface and then to radially compress and axially elongate said ring beyond elastic limit thereof and thereby cause it to take a permanent set as said ring conforms to the progressive reduction in diameter of said sizing cavity, and means for reversing the relative movement of said ring and die to remove said ring from said die.

17. The apparatus set forth in claim 16 wherein said cavity surface has a taper angle identical to that of the outer peripheral surface of said ring.

18. The apparatus set forth in claim 17 wherein said die is oriented with its axis vertical with its entrance end facing upwardly, and further including a pilot core positioned concentrically within said die cavity to provide a flat end surface flush with a flat end surface to said die to form therewith a support surface extending perpendicular to the axis of said cavity, and means for sliding said ring on said one end thereof perpendicular to the ring axis along said support surface into coaxial registry with an annular cavity defined between said pilot core and said die cavity surface, said pilot core being dimensioned so as to pilot through said ring prior to said ring being deformed by said die.

19. The apparatus set forth in claim 18 wherein said moving means is operable to terminate said increasing interference engagement travel of' said ring in said die cavity while the inner periphery of said ring is spaced from said pilot core.

20. The apparatus set forth in claim 18 wherein said ring removing means comprises an ejector annulus movable axially within said cavity to bring an end surface of said ejector flush with said flat end surfaces, said sliding means being operable to move said ring into said registry on said ejector end surface, said ejector thereupon operating to lower said ring into engagement with the sizing of said die cavity.

21. The apparatus set forth in claim 20 including support means for maintaining said die stationary, and wherein said moving means is operable to move said ring into and out of the entrance of said die cavity to accomplish said relative axial movement in both of said directions.

2% UNETED STATES PATENT OFFICE CERTIFZEATE 0F CUEETEOFN Patent No. 3,805,360 Dated April 23, 1974 Inventor(s) Alexander Brede III and Charles Robert Talmage It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Title page, item {75] after "Lansing" insert --Michigan-- and cancel "both' of" Column 2, line 55 cancel "fully" and insert --full-- Column 3, line 40 after "30" insert -until-- Column 10, linei 2l after "sizing" insert -surface Signed and sealed this 12th day of November 1974.

(SEAL) Attest:

McCOY M. GIBSONJRo C. MARSHALL DANN Attesting Officer Commissioner of Patents (2x3 UNITED STATES PATENT OFFICE CERTIFXCATE OF CORRECTION Patent No. 3,805,360 Dated April 23, 1974 Inventor(s) Alexander Brede III and Charles Robert, Talmage It is certifiedthat errorappears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 40 after "30" insert -until- Column 10, line after "sizing" insert --surface-- Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents Title page, item {75] after "Lansing" insert -Michi.ganand cancel "both of" Column 2, line 55 cancel "fully" and insert --full- Signed and sealed this 12th day of November 1974.

(SEAL) 

1. A method of sizing an out-of-round brake drum ring compacted and sintered from metal powder and having a frustoconical outer peripheral surface tapering linearly toward the axis of said ring toward one of the ends of said ring, comprising the steps of positioning the ring coaxially on a sizing die having a sizing cavity with a frustoconical peripheral surface tapered complementarily to said outer ring surface and of substantially perfect circularity for an axial distance exceeding the axial dimension of said ring, said cavity tapering from a diameter greater than to less than the outside diameter of said one end of said ring, bringing said ring into circularity by moving said ring and die axially relative to one another in the direction of increasing interference fit of said ring in said die cavity by applying axial force endwise to said ring and an opposing axial force to said die while leaving said ring unrestrained against movement in said direction except for the sliding frictional interengagement of said ring and cavity surfaces, terminating said movement after a predetermined relative axial travel of said ring along said cavity surface sufficient to first bend said outer peripheral surface of said ring into complete circumferential contact with said cavity surface throughout the axial extent of said ring surface and then to radially compress said ring beyond the elastic limit thereof and thereby cause it to take a permanent set as said ring conforms to the progressive reduction in diameter of said sizing cavity, and then reversing the relative movement of said ring and die to remove said ring from said die.
 2. The method set forth in claim 1 wherein said cavity surface and said outer peripheral surface of said ring each have identical taper angles.
 3. The method set forth in claim 1 wherein said ring is allowed to axially elongate in response to said radial compression thereof.
 4. The method set forth in claim 3 wherein the inner periphery of said ring is cylindrical and comprises the brake track of said ring.
 5. The method of claim 1 wherein the inner peripheral surface of said ring is maintained clear of any restraining aPparatus during said relative axial motion in the direction of increasing interference fit.
 6. The method set forth in claim 1 wherein said die is oriented with its axis generally vertical with its entrance end facing upwardly, and a pilot core is positioned concentrically within said die cavity to provide a flat end surface flush with a flat end surface of said die to form therewith a support surface extending perpendicular to the axis of said cavity, and wherein said step of positioning said ring includes sliding said ring on said one end thereof perpendicular to the ring axis along said support surface into coaxial registry with an annular cavity defined between said pilot core and said die cavity surface, the core piloting through said ring while said ring is being deformed by said die.
 7. The method set forth in claim 6 wherein said increasing interference engagement travel of said ring in said die cavity is terminated while the inner periphery of said ring is spaced from said pilot core.
 8. The method set forth in claim 6 wherein said positioning step further comprises elevating an ejector annulus within said cavity to bring an end surface of said ejector flush with said flat end surfaces, then sliding said ring into said registry to position the ring on said ejector end surface, and then lowering said ejector to lower said ring into engagement with the sizing surface of said die cavity.
 9. The method set forth in claim 8 wherein said drum ring has a density of about 6.7 grams per cubic centimeter.
 10. The method set forth in claim 1 wherein said taper angle of said outer periphery of said ring is in the order of five to fifteen degrees included angle.
 11. The method set forth in claim 9 wherein said ring is made by compacting and sintering a metal powder blend comprising iron, graphite and wax and adpted to provide a pearlitic microstructure.
 12. The method set forth in claim 11 wherein said drum ring has an inside diameter in the order of about five to twenty inches and an axial dimension in the order of 2 to 10 inches.
 13. The method set forth in claim 12 wherein the relative axial travel of said ring and die is in the order of 0.2 to 2.0 inches.
 14. The method set forth in claim 1 wherein said die is held stationary and said ring is moved into and out of the entrance of said die cavity to accomplish said relative axial movement in both of said directions.
 15. A method of making a brake drum ring comprising the steps of compacting a brake drum ring from metal powder blend containing primarily iron powder into a ring shape having a trapezoid radial cross section with a frustoconical outer peripheral surface tapering linearly toward the axis of said ring toward one of the ends of said ring, sintering the ring compact and then cooling the same whereby said ring may be distorted to an out-of-round condition, positioning the ring coaxially in a sizing die cavity having a frustoconical peripheral surface tapered complementarily to said outer ring surface from a diameter greater than to less than the outside diameter of said one end of said ring and being of substantially perfect circularity for an axial distance exceeding the axial dimension of said ring, bringing said ring into circularity by moving said ring and die axially relative to one another in the direction of increasing interference fit of said ring in said die cavity by applying opposing axial forces endwise to said ring and said die while leaving said ring unrestrained against movement in said direction except for the sliding frictional interengagement of said ring and cavity surfaces, terminating said movement after a predetermined relative axial travel of said ring along said cavity surface sufficient to first bend said outer peripheral surface of said ring into substantially complete circumferential contact with said cavity surface throughout the axial extent of said ring surface and then to radially compress said ring beyond the elastic limIt thereof and thereby cause it to take a permanent set as said ring conforms to the progressive reduction in diameter of said sizing cavity, and then reversing the relative movement of said ring and die to remove said ring from said die.
 16. Apparatus for sizing an out-of-round brake drum ring compacted and sintered from metal powder and having a frustoconical outer peripheral surface tapering linearly toward the axis of the ring toward one of the ends of the ring, comprising a sizing die having a sizing cavity with a frustoconical peripheral surface tapered complementarily to the outer surface of the ring and of substantially perfect circularity for an axial distance exceeding the axial dimension of the ring, said cavity tapering from a diameter greater than to less than the outside diameter of said one end of the ring, means for moving said ring and die axially relative to one another in the direction of increasing interference fit of said ring in said die cavity, said moving means being adapted to apply axial force endwise to said ring and said die while leaving said ring unrestrained against movement in said direction except for the sliding frictional interengagement of said ring and cavity surfaces, said moving means being operable to terminate said movement after a predetermined relative axial travel of said ring along said cavity surface sufficient to first bend said outer peripheral surface of said ring into substantially complete circumferential contact with said cavity surface throughout the axial extent of said ring surface and then to radially compress and axially elongate said ring beyond elastic limit thereof and thereby cause it to take a permanent set as said ring conforms to the progressive reduction in diameter of said sizing cavity, and means for reversing the relative movement of said ring and die to remove said ring from said die.
 17. The apparatus set forth in claim 16 wherein said cavity surface has a taper angle identical to that of the outer peripheral surface of said ring.
 18. The apparatus set forth in claim 17 wherein said die is oriented with its axis vertical with its entrance end facing upwardly, and further including a pilot core positioned concentrically within said die cavity to provide a flat end surface flush with a flat end surface to said die to form therewith a support surface extending perpendicular to the axis of said cavity, and means for sliding said ring on said one end thereof perpendicular to the ring axis along said support surface into coaxial registry with an annular cavity defined between said pilot core and said die cavity surface, said pilot core being dimensioned so as to pilot through said ring prior to said ring being deformed by said die.
 19. The apparatus set forth in claim 18 wherein said moving means is operable to terminate said increasing interference engagement travel of said ring in said die cavity while the inner periphery of said ring is spaced from said pilot core.
 20. The apparatus set forth in claim 18 wherein said ring removing means comprises an ejector annulus movable axially within said cavity to bring an end surface of said ejector flush with said flat end surfaces, said sliding means being operable to move said ring into said registry on said ejector end surface, said ejector thereupon operating to lower said ring into engagement with the sizing of said die cavity.
 21. The apparatus set forth in claim 20 including support means for maintaining said die stationary, and wherein said moving means is operable to move said ring into and out of the entrance of said die cavity to accomplish said relative axial movement in both of said directions. 